A negative glow lamp typically is comprised of a light transmitting envelope containing a noble gas and mercury with a phosphor coating on an inner surface of the envelope which is adapted to admit visible light upon absorption of ultraviolet radiation that occurs when the lamp is excited. The lamp is excited by means of the application of a voltage between the lamp electrodes. Current flows between the electrodes after a certain potential is applied to the electrodes, commonly referred to as the breakdown voltage. An elementary explanation of the phenomenon is that the gas between the electrodes becomes ionized at a certain voltage, conducts current, and emits ultraviolet radiation. Examples of typical glow discharge lamps are found in U.S. Pat. No. 2,067,129 to Marden; U.S. Pat. No. 3,814,971 to Bhattacharya; and U.S. Pat. No. 4,408,141 to Byszewski et al.
When operating commercially on alternating current, a typical fluorescent lamp will generally contain a pair of electrodes of similar construction. Each electrode will act as cathode during one-half of the cycle and as anode during the other half. To avoid overheating during the anode portion of the cycle, anode probes (sometimes referred to as auxiliary electrodes) are added to the electrode structure to collect electrons during the positive half-cycle. The anode probes are electrically connected to the ends of the electrodes.
An example of a fluorescent lamp containing anode probes is shown in U.S. Pat. No. 4,013,914, which issued to Clune et al on Mar. 22, 1977. As illustrated therein, an L-shaped wire probe (coated with a dielectric material) is electrically connected to each lead-in wire adjacent the ends of the electrode and extends parallel to the electrode.
Although the L-shaped probes of Clune et al function effectively, the L-shaped probe configuration presents several disadvantages. For example, when the probes of Clune et al are mounted in a single-ended, negative glow discharge lamp and oriented in a common plane with a pair of parallelly-spaced electrodes, a fraction of fast electrons accelerated in the cathode fall are allowed to collide into the probes prior to exciting mercury atoms. As a result, a loss in lamp efficacy occurs. Moreover, the particular probe configuration taught by Clune et al can absorb a fraction of the light generated by excited mercury atoms and can also cause a loss in lamp efficacy by decreasing the anode fall.